1. Field of the Invention
The present invention relates to a device for the selection, metering and delivery of liquids, in particular treatment liquids for industrial laundry washers.
2. Description of the Prior Art
In industrial laundry washers, opposed from domestic laundry washers, there are used liquid treatment materials, such as detergents, softeners, optical bleaches, disinfectants, rather than such materials in powder form.
Normally, the dosages of these components were prepared manually on volume or weight base and then these were inserted by an operator in the washing machine at selected times of the washing cycles. These systems have the inconvenience of a low dosage precision, need of manpower and dead times.
Recently, automatic metering apparatus have been introduced. The most common of these apparatus includes a series of positive displacement pumps of the membrane type for the delivery of treatment liquids to the washing machine.
Even if these kinds of apparatus provide appreciable advantages with respect to the manual dosing systems, the metering precision is not very high for several reasons; the quantity of liquid that is delivered is controlled by the number of pumping strokes and for each pumping stroke the pumps deliver a constant volume. Consequently, the adjustment of the metering may be made only in discrete steps. Moreover, the number of the pumping strokes is controlled through the operation time of the pump. This means that with liquids having a different density or viscosity, the pumping rate may be modified by the mechanical load imposed by the characteristics of the pumped liquid with a consequence lack of precision in the metering.
It should be remarked that there are available on the market metering pumps that are very sophisticated and that provide a very great precision. There cost is, however, prohibitive for industrial uses of this kind.
The purpose of the present invention is, therefore, the one of providing a device for the selection, metering and delivery of treatment liquids that shows a high metering precision, a very simple principle of operation and low requirements of maintenance and low cost.